Semiconductor devices are formed on semiconductor wafers by performing a number of fabrication processes. For example, layers are formed by depositing materials, layers are patterned by employing etch processes, trenches are formed in substrates and filled with material, surfaces of the devices are planarized and cleaned, and the like.
As a result of these fabrication processes, residues, including debris and contaminants, can be left on semiconductor wafers. For example, polishing/planarizing processes are typically employed to planarize layers deposited on the wafer. The polishing processes employ a chemical mechanical slurry and pad that mechanically and chemically planarize the wafer surfaces. After polishing, slurry residue is generally cleaned or scrubbed from wafer surfaces by mechanical scrubbing devices, such as polyvinyl acetate (PVA) brushes. These conventional cleaning processes tend to remove a substantial portion of the slurry residue, but some particles can remain as residue, particularly on edges of the wafer.
Another source of residue is due to metal film deposition. A clamp ring may be employed to secure a wafer to a heated pedestal within a deposition chamber to shield wafer edges from film disposition, such as to prevent metal from depositing along wafer edges and shorting subsequently formed devices as a result. Because the wafer and clamp ring possess different coefficients of thermal expansion, each expands at a different rate during metal film deposition. The shear force between the clamp ring and the wafer's edge may also generate edge particles that serve as a residue source.
Patterning processes employ photoresist masks that can leave ashed resist as contamination or residue afterwards. Additionally, deposited materials, including metals and non-metals, can undesirably deposit on wafer edges as residue. Still other contaminants can be formed on the wafer edges from doping or ion implantation processes.
These residues can be sources of defects in later formed semiconductor structures. For example, layers can be formed on the residues or contaminants leading to blistering, delamination, undesired voids, and the like.
Some types of residue adhere to wafer edges more strongly than others and are, therefore, more troublesome to remove and prevent from contaminating subsequent processes. For example, wafer holding mechanisms, including pedestals, are often comprised at least partly of carbon material. The wafer holding mechanisms frequently grab wafers on their edges. As a result, the wafer holding mechanisms can leave carbon residue that is strongly adhered to the wafer edges. Such strongly adhered residue is not generally removable by conventional mechanisms.